1. Field of the Invention
The present invention relates to paste for a transparent insulating film, a plasma display panel, a method of manufacturing paste, a method of manufacturing a transparent insulating film, and a method of manufacturing a plasma display panel.
2. Description of the Related Art
First, referring to FIG. 1 showing a structural diagram of a plasma display panel, the configuration of a conventional plasma display panel will be discussed.
The plasma display panel is constituted by scanning electrodes 1, maintaining electrodes 2, a black stripe 3, a transparent insulating film 4, an MgO film 5, a phosphor 6, a rib 7, a ground surface dielectric 8, and data electrodes 9. Voltage is applied between the scanning electrodes 1 and the data electrodes 9 to discharge, and light emitted from the phosphor 6 passes through the transparent insulating film 4 and acts as image light.
Light can be emitted at a desired position of the phosphor (equivalent to a pixel) to obtain an image by selecting desired data electrodes 9 and scanning electrodes 1 and applying voltage.
The transparent insulating film 4 is about 50 μm in thickness and requires dielectric withstand voltage characteristics and optical characteristics. To be specific, dielectric withstand voltage can be obtained under a voltage of about AC 400V and an optical clouding degree (Hayes value, simply referred to as Hayes) is minimized.
A method of manufacturing a conventional transparent film will be discussed. A conventional transparent insulating film is obtained as follows: paste is manufactured by using powder glass having D10 of 0.5 μm, D50 of 1.6 μm, and D90 of 3 μm, the paste is applied by screen printing and die coating with a thickness of 50 μm, and drying and firing are performed.
Although a transparent insulating film manufactured by such a method has a dielectric withstand voltage of a passing standard, large Hayes of about 30% appears. The Hayes mainly depends upon a particle size of powder glass used as a material. Besides, a plasma display having a transparent insulating film with large Hayes is configured as if an image was seen through ground glass. Hence, an image becomes less sharp.
Additionally, when powder glass with D10 of 0.5 μm, D50 of 1.0 μm, and D90 of 1.5 μm is used, Hayes is expected to decrease, thereby improving the performance of a plasma display. However, particles are likely to cling together because they are small. Thus, it has been difficult for a conventional method to achieve dispersion to a first particle level, that is, to disperse particles one by one. Namely, although powder has a particle size distribution of FIG. 4(a), when paste is manufactured by a conventional method, a particle size distribution is shifted to a larger one indicated by a solid line of FIG. 4(b).
Further, a strong dispersing process of sand mill and the like is provided as a means of forcefully dispersing particles. However, such a dispersing process destroys particles of powder glass during dispersion. Moreover, physical properties are changed when particles are destroyed, resulting in deterioration in characteristics such as transmittance of light and dielectric withstand voltage. Namely, although powder has a particle size distribution of FIG. 4(a), when paste is manufactured by the conventional method, a particle size distribution is distorted as indicated by a broken line of FIG. 4(b).